An elegant noise measurement technique was developed as part of radar research during WW II by Dr. Dicke. This approach alternately measured the net power in a given passband's bandwidth of the system of interest versus a calibrated noise source.
An extension of this approach is described in “A Noise-Adding Radiometer for the Parkes Antenna”, T. J. Brunzie, TDA Progress Report 42-92, October-December 1987. This approach allowed continuous monitoring of the passband total power. As with Dr. Dicke's approach, the total power in a bandpass is measured.
The next-generation GPS control system (OCX) requires monitor receivers to measure the GPS signal levels. The receivers measure the signal to noise ratios (SNRs), but the noise level is required in addition in order to deduce the signal levels. The initially proposed means to measure the noise for these monitor stations was a process to measure the SNR of each code, then use the Automatic Gain Control (AGC) level to determine the bandpass power in each of the receiver's baseband spectra. Since the AGC operates after about 100 dB of amplification, variations of gain in the receiver would exceed the error budget for code power measurements. Also, the AGC measures the noise in the total bandpass, while the SNR measures the noise which has been filtered by the receiver's local model of the transmitted ranging code. The latter is what is needed to translate from SNR to signal power. The current invention measures the noise power after it has been filtered by the code model, and is therefore what is needed to translate the measured SNR to the received signal power.
There is a need for systems and methods that provide and take advantage of a more accurate measure of noise temperature experienced by wireless receivers during operation.